A power supply controller used as a so-called high-side driver is conventionally provided, in which an N-channel MOSFET for current control is disposed between a positive power source and a load as shown in JP-A-2001-217696. In the power supply controller, the gate voltage should be higher than (or generally about double) the power supply voltage in order that the MOSFET is adequately turned ON (i.e., turned to a conductive state). For achieving this, a gate driver circuit (or a charge pump circuit) should be provided. Specifically, when an ON signal is externally inputted to the power supply controller, the gate driver circuit generates a higher voltage as an output voltage from an input voltage that is based on the power supply voltage, and applies the output voltage to the gate so as to turn ON the MOSFET. Some of such power supply controllers have an overcurrent protective function for forcibly turning OFF the MOSFET in response to a current anomaly wherein a load current passing through the MOSFET exceeds a predetermined threshold due to a load anomaly such as short-circuiting of the load.
In the case that the MOSFET is turned ON due to an ON signal applied when a load anomaly has occurred as described above, it is desirable to turn the MOSFET to a shutoff state early. For achieving this, the charge rate of the gate driver circuit should be as high as possible so that the load current exceeds the above threshold early. However, if the charge rate of the gate driver circuit as a constant rate is set to be high in the conventional power supply controller, the MOSFET is charged rapidly even when it is turned ON during a normal state in which a load anomaly has not occurred. This will result in noise generation due to precipitous change of the load current. Conversely, if the charge rate of the charging circuit is set to be lower, noise generation can be suppressed. However, the problem arises that the MOSFET will be slow to turn OFF after the MOSFET is turned ON during a load anomaly, which will result in great power loss (or switching loss).
Thus, there is a need in the art for a power supply controller enabling reduction of power loss during a load anomaly while suppressing noise generation.